Electromagnetic wave-absorbing thermally conductive sheet

Abstract

Provided is an electromagnetic wave-absorbing thermally conductive sheet excellent in thermal conductivity and in characteristics of absorbing electromagnetic waves of a millimeter wave band.　An electromagnetic wave-absorbing thermally conductive sheet 1 comprises: a binder component 11; and a powder 12. The electromagnetic wave-absorbing thermally conductive sheet 1 has a thermal conductivity of 3 W / mK or more in the thickness direction when the sheet is compressed so as to have a thickness of 80%, and a dielectric loss of 3000 dB / m or more at a frequency of 28 GHz. The powder 12 preferably contains a powder (A) 12a having a median diameter of more than 20 μm but not more than 130 μm and a powder (B) 12b having a median diameter of 1-20 μm.

Description

Electromagnetic wave absorbing and thermally conductive sheet

[0001] The present invention relates to an electromagnetic wave absorbing and heat conductive sheet.

[0002] In recent years, advances in electronics have led to the widespread use of heat-generating components in electronic devices, such as power devices. To control electronic circuits, it is important to dissipate the heat from these heat-generating components and cool the entire system. Thermally conductive sheets (heat-dissipating sheets) are placed, for example, between the heat-generating components and heat-dissipating fins or metal plates, and are tightly pressed against the heat-generating components to eliminate gaps. These sheets exhibit thermal conductivity, transferring heat generated by the heat-generating components to the heat-dissipating fins, etc., thereby dissipating heat from the entire system.

[0003] The thermally conductive sheet is composed of, for example, a thermally conductive inorganic filler and a resin. The inorganic filler may be inexpensive aluminum hydroxide or aluminum oxide (alumina), or silicon carbide, boron nitride, or aluminum nitride, which are expected to have higher thermal conductivity. The resin may be, for example, an acrylic resin or a urethane resin.

[0004] Thermally conductive sheets are increasingly being required to provide protection against electromagnetic waves. Sheets capable of absorbing electromagnetic waves and converting them into heat, as well as having thermal conductivity (electromagnetic wave-absorbing thermally conductive sheets), are known as sheets that provide protection against electromagnetic waves and have thermal conductivity. Electromagnetic wave-absorbing thermally conductive sheets are generally produced by highly loading powder into an organic binder component. Known examples of such electromagnetic wave-absorbing thermally conductive sheets include those disclosed in Patent Document 1.

[0005] Japanese Patent Application Laid-Open No. 2022-52761

[0006] In recent years, electromagnetic wave-absorbing heat-conductive sheets have been required to have excellent electromagnetic wave absorption properties in the millimeter wave band. However, conventional electromagnetic wave-absorbing heat-conductive sheets have used magnetic materials with low permeability and low dielectric constant in the millimeter wave band, which has not provided sufficient electromagnetic wave absorption properties in the millimeter wave band. Furthermore, such magnetic materials have low thermal conductivity, which has resulted in poor thermal conductivity of the electromagnetic wave-absorbing heat-conductive sheets.

[0007] Therefore, an object of the present invention is to provide an electromagnetic wave absorbing, heat conductive sheet that is excellent in thermal conductivity and electromagnetic wave absorption properties in the millimeter wave band.

[0008] The present invention provides an electromagnetic wave absorbing, heat conductive sheet which contains a binder component and a powder, and which has a thermal conductivity of 3 W / mK or more in the thickness direction when compressed to 80% of its original thickness, and a dielectric loss of 3000 dB / m or more at a frequency of 28 GHz.

[0009] The powder preferably contains silicon carbide and / or zinc oxide.

[0010] It is preferable that the content of the binder component is 2 to 40% by mass, and the content of the powder is 60 to 98% by mass.

[0011] The powder preferably contains powder (A) having a median diameter of more than 20 μm and not more than 130 μm, and powder (B) having a median diameter of 1 to 20 μm.

[0012] The powder preferably contains powder (C) having a median diameter of less than 1 μm.

[0013] The powder may contain powder (C) having a median diameter of less than 1 μm, and it is preferable that, relative to 100% by mass of the total amount of the powder in the electromagnetic wave absorbing heat conductive sheet, the content of powder (A) is 30 to 90% by mass, the content of powder (B) is 10 to 60% by mass, and the content of powder (C) is 30% by mass or less.

[0014] The binder component is preferably a silicone-based resin.

[0015] The electromagnetic wave absorbing and heat conductive sheet of the present invention has excellent thermal conductivity and millimeter wave absorption properties.

[0016] 1 is a partial cross-sectional view showing one embodiment of an electromagnetic wave-absorbing heat-conductive sheet of the present invention.

[0017] [Electromagnetic Wave-Absorbing Heat-Conductive Sheet] The electromagnetic wave-absorbing heat-conductive sheet of the present invention contains at least a binder component and a powder.

[0018] The electromagnetic wave-absorbing heat-conductive sheet is preferably in a form that does not involve a substrate (substrate layer), i.e., is so-called "substrate-less." Note that the "substrate (substrate layer)" does not include a release sheet that is peeled off when the electromagnetic wave-absorbing heat-conductive sheet is used.

[0019] The electromagnetic wave absorbing heat conductive sheet has a thermal conductivity in the thickness direction of 3 W / mK or more, preferably 3.5 W / mK or more, and more preferably 4 W / mK or more when compressed to 80% of its thickness (20% compression). The thermal conductivity of 3 W / mK or more provides excellent thermal conductivity and heat dissipation in the thickness direction.

[0020] The electromagnetic wave absorbing heat conductive sheet has a dielectric loss of 3000 dB / m or more at a frequency of 28 GHz, preferably 4000 dB / m or more, and more preferably 5000 dB / m or more. The dielectric loss of 3000 dB / m or more provides excellent electromagnetic wave absorption performance in the millimeter wave band.

[0021] The electromagnetic wave-absorbing heat-conductive sheet may include a release sheet. The release sheet may be provided on only one side of the electromagnetic wave-absorbing heat-conductive sheet, or on both sides. Examples of the release sheet include a film formed from a low-adhesion resin, and a sheet provided with a release-treated layer on the surface of the film. The release sheet is peeled off and removed when the electromagnetic wave-absorbing heat-conductive sheet is used.

[0022] (Binder component) The binder component is a component that forms the matrix of the electromagnetic wave absorbing heat conductive sheet. Examples of the binder component include resins (binder resins) such as thermoplastic resins, thermosetting resins, and active energy ray curable resins. Only one type of binder component may be used, or two or more types may be used.

[0023] Examples of the thermoplastic resin include polystyrene resins, vinyl acetate resins, polyester resins, polyolefin resins (e.g., polyethylene resins, polypropylene resin compositions, etc.), polyimide resins, acrylic resins, etc. One type of the thermoplastic resins may be used alone, or two or more types may be used.

[0024] The thermosetting resin includes both a resin having thermosetting properties (thermosetting resin) and a resin obtained by curing the thermosetting resin. Examples of the thermosetting resin include silicone resin, phenolic resin, epoxy resin, urethane resin, urethane urea resin, melamine resin, alkyd resin, polyimide resin, and acrylic resin. Only one type of the thermosetting resin may be used, or two or more types may be used.

[0025] The active energy ray curable resin includes both a resin that can be cured by active energy ray irradiation (active energy ray curable resin) and a resin obtained by curing the active energy ray curable resin.The active energy ray curable resin is not particularly limited, but for example, a polymer of a polymerizable compound having at least two (meth)acryloyloxy groups in the molecule can be used.The active energy ray curable resin may be used alone or in combination of two or more.

[0026] Among the above binder resins, thermosetting resins are preferred, and silicone resins are more preferred from the viewpoint of excellent thermal conductivity, heat resistance, and insulation. As the silicone resin, known or commonly used silicone resins used in thermally conductive sheets can be used. As the silicone resin, two-component curing silicone resins are preferred from the viewpoint of being able to disperse powder well without using a solvent. Only one type of silicone resin may be used, or two or more types may be used.

[0027] The content of the binder component is preferably 2% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, relative to the total amount (100% by mass) of the electromagnetic wave-absorbing heat conductive sheet. When the content is 2% by mass or more, the electromagnetic wave-absorbing heat conductive sheet is less likely to become brittle and has excellent film-forming properties. The content is preferably 40% by mass or less. When the content is 40% by mass or less, the thermal conductivity and electromagnetic wave absorption properties of the electromagnetic wave-absorbing heat conductive sheet are improved. In particular, it is preferable that the content of the silicone resin be within the above range.

[0028] (Powder) By including the powder, the electromagnetic wave absorbing heat conductive sheet exhibits thermal conductivity and electromagnetic wave absorbing properties. The powder is preferably a powder having thermal conductivity and electromagnetic wave absorbing properties. Only one type of powder may be used, or two or more types may be used.

[0029] The powder may be appropriately selected from those having thermal conductivity or electromagnetic wave absorption properties. Examples of the powder include inorganic powders such as silicon carbide, zinc oxide, alumina, magnesium oxide, aluminum nitride, boron nitride, silica, iron-based alloy powders such as silicon carbide, zinc oxide, alumina, magnesium oxide, aluminum nitride, boron nitride, silica, Fe—Si alloy, Fe—Al alloy, Fe—Si—Al alloy (Sendust), Fe—Si—Cr alloy, Fe—Ni alloy (Permalloy), Fe—Ni—Co alloy (Mumetal), Fe—Ni—Mo alloy (Supermalloy), Fe—Co alloy, Fe—Si—Al—Cr alloy, Fe—Si—B alloy, and Fe—Si—Co—B alloy, and carbonyl iron powder. Other examples include ferrite powders such as spinel ferrites such as Mn-Zn ferrite, Mn-Mg-Zn ferrite, Mg-Cu-Zn ferrite, Ni-Zn ferrite, Ni-Cu-Zn ferrite, and Cu-Zn ferrite, and hexagonal ferrites such as W-type, Y-type, Z-type, and M-type.

[0030] The powder preferably contains silicon carbide and / or zinc oxide, and more preferably silicon carbide. Silicon carbide and zinc oxide have excellent thermal conductivity and high dielectric constant, so the electromagnetic wave absorbing heat conductive sheet has particularly good thermal conductivity and millimeter wave absorption characteristics. Silicon carbide preferably has an α-type crystal system.

[0031] The shape of the powder is not particularly limited, and examples thereof include spherical (including spherical and elliptical), flake (scale-like), dendritic, blocky, flat, acicular, irregular (polyhedral), etc. Among these, spherical is preferred from the viewpoint of improving the packing property in the electromagnetic wave-absorbing thermally conductive sheet and providing superior thermal conductivity.

[0032] The powder is particularly preferably one in which the number of small corners on the surface of the primary particles is 2.5 or less (preferably 2.2 or less, more preferably 1.2 or less) per primary particle. The small corners are corners present on the outline of the primary particles in a projected image of the primary particles, and two times the radius of curvature of the small corners is 1 / 5 or less of the Heywood diameter of the projected image of the primary particles. The powder is sometimes referred to as a "high-roundness powder."

[0033] In the highly rounded powder, the corner is a point where the outline of the primary particle in a projected image of the primary particle changes at an angle, and the angle is an interior angle facing inward of the outline of the primary particle that is greater than 0° and less than 180°. The outline forming the corner may be straight or rounded. The Heywood diameter, also referred to as the diameter of a circle equivalent to the projected area of ​​a particle determined by image analysis, is the diameter of a circle having the same area as the projected area of ​​the particle.

[0034] The high-circularity powder has few small corners and the shape of the primary particles is closer to a perfect sphere, so by using the high-circularity powder as a powder, the powder packing rate can be increased, and the thermal conductivity and electromagnetic wave absorption properties can be further improved. Furthermore, the high-circularity powder does not easily increase the viscosity when added to a binder component, and has excellent fluidity and handleability. In particular, it is preferable to use silicon carbide as a high-circularity powder.

[0035] The powder preferably contains two or more types of powders with different median diameters, from the viewpoint of increasing the powder packing rate and improving the thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band of the electromagnetic wave absorbing heat conductive sheet. That is, the powder preferably has two or more peak tops in the particle size distribution.

[0036] The powder may be surface-treated or may not be surface-treated. Examples of the surface treatment agent used for the surface treatment include silane coupling agents. When the powder is surface-treated with a silane coupling agent, it has good dispersibility in the binder component (particularly, silicone-based resin) that is the matrix of the electromagnetic wave-absorbing, heat-conductive sheet, and is superior in fillability and film-forming properties. Only one type of silane coupling agent may be used, or two or more types may be used.

[0037] Examples of the silane coupling agent include silane coupling agents having functional groups other than alkoxy groups (functional group-containing silane coupling agents), such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane; and silane coupling agents having no functional groups other than alkoxy groups (functional group-free silane coupling agents), such as n-octyltriethoxysilane and n-decyltrimethoxysilane. Among these, non-functional group-containing silane coupling agents are preferred, from the viewpoint of good wettability with alumina powder and the expected improvement in bulk strength and flexibility of the electromagnetic wave absorbing thermally conductive sheet, and more preferably silane coupling agents in which the terminal other than the alkoxy group is an alkyl group (terminal alkyl group-containing silane coupling agents), and particularly preferably n-octyltriethoxysilane.

[0038] The powder preferably contains a powder having a median diameter of more than 20 μm and not more than 130 μm. By including such a powder, the electromagnetic wave absorbing and thermally conductive sheet has better thermal conductivity and electromagnetic wave absorption properties in the millimeter wave band. In this specification, a powder having a median diameter of more than 20 μm and not more than 130 μm may be referred to as "powder (A)." The median diameter of powder (A) is preferably 25 to 100 μm, more preferably 30 to 80 μm.

[0039] The powder (A) can be appropriately selected from the types and shapes exemplified and described above. Among these, the powder (A) is preferably silicon carbide and / or zinc oxide, and particularly preferably silicon carbide. Furthermore, the powder (A) is preferably spherical or highly spherical. By using such powder (A), the thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band of the electromagnetic wave absorbing thermally conductive sheet are further improved.

[0040] The powder preferably contains powder having a median diameter of 1 to 20 μm. By including such powder, the electromagnetic wave absorbing heat conductive sheet has better thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band. In particular, by including powder (A) together with the powder, the powder filling rate in the electromagnetic wave absorbing heat conductive sheet is increased, and the electromagnetic wave absorbing heat conductive sheet has even better thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band. In this specification, powder having a median diameter of 1 to 20 μm may be referred to as "powder (B)." The median diameter of powder (B) is preferably 2 to 15 μm.

[0041] Powder (B) can be appropriately selected from the types and shapes exemplified and described above. Among these, powder (B) is preferably silicon carbide and / or zinc oxide, and particularly preferably silicon carbide. Furthermore, powder (B) is preferably spherical or highly spherical. By using such powder (B), the thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band of the electromagnetic wave absorbing thermally conductive sheet are further improved.

[0042] The powder may contain powder with a median diameter of less than 1 μm. By including such powder, the electromagnetic wave-absorbing heat-conductive sheet has better thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band. In particular, by including powder (A) and / or powder (B) together, the powder filling rate in the electromagnetic wave-absorbing heat-conductive sheet is increased, and the electromagnetic wave-absorbing heat-conductive sheet has even better thermal conductivity and electromagnetic wave absorption characteristics in the millimeter wave band. In this specification, powder with a median diameter of less than 1 μm may be referred to as "powder (C)." The median diameter of powder (C) is preferably 0.01 μm or more and less than 1 μm, more preferably 0.1 to 0.6 μm.

[0043] In this specification, the median diameter (D50) of a powder is the average primary particle diameter on a number basis measured by a laser diffraction / scattering method.

[0044] The powder (C) can be appropriately selected from the types and shapes exemplified and described above. Among these, the powder (C) is preferably one or more selected from the group consisting of silicon carbide, zinc oxide, and alumina. Furthermore, the powder (C) is preferably spherical. By using such powder (C), the powder filling rate in the electromagnetic wave-absorbing thermally conductive sheet is further increased, resulting in even better thermal conductivity of the electromagnetic wave-absorbing thermally conductive sheet.

[0045] The filling rate (content ratio) of the powder in the electromagnetic wave-absorbing heat conductive sheet is preferably 60% by mass or more relative to the total amount (100% by mass) of the electromagnetic wave-absorbing heat conductive sheet. When the content ratio is 60% by mass or more, the powder filling rate in the electromagnetic wave-absorbing heat conductive sheet is high, resulting in superior thermal conductivity and electromagnetic wave absorption properties. The content ratio is preferably 98% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less. When the content ratio is 98% by mass or less, the electromagnetic wave-absorbing heat conductive sheet is less likely to become brittle, resulting in excellent film-forming properties when producing the electromagnetic wave-absorbing heat conductive sheet. Furthermore, it is preferable that the total proportion of powder (A), powder (B), and powder (C) be within the above range.

[0046] The content of powder (A) in the electromagnetic wave-absorbing heat-conductive sheet is preferably 30 to 90 mass%, more preferably 40 to 80 mass%, and even more preferably 50 to 70 mass%, relative to the total amount (100 mass%) of the powder in the electromagnetic wave-absorbing heat-conductive sheet.

[0047] The content of powder (B) in the electromagnetic wave-absorbing heat-conductive sheet is preferably 10 to 60 mass %, more preferably 20 to 50 mass %, and even more preferably 30 to 45 mass %, relative to the total amount (100 mass %) of the powder in the electromagnetic wave-absorbing heat-conductive sheet.

[0048] The content of powder (C) in the electromagnetic wave-absorbing heat conductive sheet is preferably 30% by mass or less, but may be 20% by mass or less, or 10% by mass or less, relative to the total amount (100% by mass) of the powder in the electromagnetic wave-absorbing heat conductive sheet, or the sheet may not contain powder (C). When powder (C) is contained, the content may be 1% by mass or more, or 5% by mass or more, or 10% by mass or more.

[0049] The total content of powder (A), powder (B), and powder (C) in the electromagnetic wave-absorbing heat-conductive sheet is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the total amount (100% by mass) of the powder in the electromagnetic wave-absorbing heat-conductive sheet. When the content is within the above range, the thermal conductivity and electromagnetic wave absorption properties are even better. Note that when at least one powder of powders (A) to (C) is not included, the content refers to the total content of the powders (A) to (C) contained.

[0050] The mass ratio of powder (B) to powder (A) in the electromagnetic wave-absorbing heat-conductive sheet [powder (B) / powder (A)] is preferably 0.1 to 0.9, more preferably 0.4 to 0.85, and even more preferably 0.6 to 0.8. When the mass ratio is within the above range, the filling rate of the powder in the electromagnetic wave-absorbing heat-conductive sheet is high, and the thermal conductivity and electromagnetic wave absorption properties are even more excellent.

[0051] The mass ratio of powder (C) to the total of powder (A) and powder (B) in the electromagnetic wave-absorbing heat-conductive sheet [powder (C) / (powder (A) + powder (B)]] is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.15 or less. When powder (C) is contained, the mass ratio is preferably 0.05 or more, more preferably 0.08 or more. When the mass ratio is within the above range, the filling rate of the powder in the electromagnetic wave-absorbing heat-conductive sheet is high, and the thermal conductivity and electromagnetic wave absorption properties are even better. Note that when the electromagnetic wave-absorbing heat-conductive sheet does not contain one of powder (A) and powder (B), the mass ratio is the mass ratio of powder (C) to the other powder.

[0052] The content of silicon carbide and / or zinc oxide (particularly silicon carbide) relative to the total amount (100% by mass) of powder (A) and powder (B) in the electromagnetic wave-absorbing heat-conductive sheet is preferably 80% by mass or more, more preferably 90% by mass or more. When the content is within the above range, the thermal conductivity and electromagnetic wave absorption properties are even better. Note that when the electromagnetic wave-absorbing heat-conductive sheet does not contain one of powder (A) and powder (B), the content is the content relative to the total amount of the other powder.

[0053] The content of silicon carbide and / or zinc oxide (particularly silicon carbide) relative to the total amount (100% by mass) of powder in the electromagnetic wave-absorbing heat conductive sheet is preferably 80% by mass or more, more preferably 90% by mass or more. When the content is within the above range, the sheet has even better thermal conductivity and electromagnetic wave absorption properties.

[0054] The electromagnetic wave-absorbing, heat-conductive sheet may contain other components in addition to the above components, as long as the intended effects of the present invention are not impaired. Examples of the other components include those contained in known or commonly used electromagnetic wave-absorbing, heat-conductive sheets. Examples of the other components include curing accelerators, plasticizers, flame retardants, antifoaming agents, viscosity modifiers, antioxidants, diluents, anti-settling agents, colorants, leveling agents, coupling agents, UV absorbers, tackifying resins, and anti-blocking agents. One or more of the other components may be used.

[0055] (Electromagnetic wave-absorbing heat-conductive sheet) Figure 1 is a cross-sectional schematic diagram showing one embodiment of the electromagnetic wave-absorbing heat-conductive sheet of the present invention. As shown in Figure 1, the electromagnetic wave-absorbing heat-conductive sheet 1 includes a binder component 11, which is a matrix component, and powder 12 dispersed in the binder component 11. The powder 12 consists of three types: powder (A) 12a, powder (B) 12b, and powder (C) 12c. Release sheets 2 and 3 are provided on both sides of the electromagnetic wave-absorbing heat-conductive sheet 1, and the electromagnetic wave-absorbing heat-conductive sheet 1 is sandwiched between the two release sheets 2 and 3.

[0056] The electromagnetic wave absorbing and heat conductive sheet has a thickness of, for example, 0.1 to 10 mm, preferably 0.3 to 5 mm, and more preferably 0.5 to 2 mm.

[0057] The method for producing the electromagnetic wave absorbing heat conductive sheet (film formation method) is not particularly limited, and any known or commonly used film formation method or molding method for a molded body can be used.

[0058] The electromagnetic wave-absorbing, heat-conductive sheet can be produced, for example, by applying a composition containing the above-mentioned various components to the release-treated surface of a release sheet to form a coating layer, and then drying and curing the coating layer by heating. Heating may be carried out with the release-treated surface of a release sheet further attached to the coating layer.

[0059] The composition includes a binder component and a powder. When two or more types of powders are used, the powders may be mixed in advance and then mixed with the binder component, or the two or more types of powders and the binder component may be mixed simultaneously. The composition is preferably in the form of a paste that does not contain an organic solvent.

[0060] The method for producing a sheet of the above composition is not particularly limited, and known coating methods such as a sandwich method in which a material is placed between release sheets coated with a release agent and laminated using a roll laminator, a hot press molding machine, or an extruder can be used.

[0061] The electromagnetic wave absorbing and heat conductive sheet of the present invention has excellent thermal conductivity and millimeter wave absorption properties.

[0062] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The content of each component shown in the tables is expressed in "parts by mass" unless otherwise specified.

[0063] Example 1 Silicon carbide particles (A), silicon carbide particles (B), and alumina particles (C) were mixed in the mass proportions shown in Table 1, and a silane coupling agent (product name "BS1601", n-octyltriethoxysilane, manufactured by Wacker Asahi Kasei Silicones Co., Ltd.) was added. The particles were surface-treated with the silane coupling agent by a dry method to produce Particle Composition 1. Particle Composition 1 was mixed with a thermosetting silicone resin (a two-component addition reaction silicone resin having a mechanism for crosslinking a polymer having vinyl groups and a polymer having Si—H groups by hydrosilylation under a platinum catalyst) as a binder component in the mass proportions shown in Table 1 to produce a resin paste. Subsequently, the resin paste was placed between the release-treated surfaces of two release sheets and laminated using a roll laminator to produce a laminate of [release sheet / resin paste layer / release sheet]. Three different film thicknesses were produced using three different spacers (0.8 mm, 1.5 mm, and 2.0 mm). The laminate was then heated at 90°C for 30 minutes to thermally harden the resin paste layer, thereby producing the electromagnetic wave absorbing heat conductive sheet of Example 1 as a laminate of [release sheet / electromagnetic wave absorbing heat conductive sheet / release sheet].

[0064] Examples 2 to 5 and Comparative Examples 1 and 2 Electromagnetic wave absorbing heat conductive sheets of Examples 2 to 5 and Comparative Example 1 were produced in the same manner as Example 1, except that the types and blending amounts of powders used were changed as shown in Table 1. Note that for Comparative Example 2, sheet molding was not possible.

[0065] The particles shown in the table are as follows: <Powder (A)> Silicon carbide particles (A): median diameter 74.5 μm, highly circular powder Zinc oxide particles (A): median diameter 39 μm, spherical Alumina particles (A): median diameter 46 μm, spherical <Powder (B)> Silicon carbide particles (B1): median diameter 12 μm, highly circular powder Silicon carbide particles (B2): median diameter 4 μm, highly circular powder with angular sides or points, not corresponding to highly circular powder Zinc oxide particles (B): median diameter 4.7 μm, spherical Alumina particles (B): median diameter 6.4 μm, spherical <Powder (C)> Alumina particles (C): median diameter 0.3 μm, spherical

[0066] (Evaluation) The electromagnetic wave absorbing and heat conductive sheets obtained in the examples and comparative examples were evaluated as follows, and the evaluation results are shown in the table.

[0067] (1) Thermal Conductivity Using a thermal property measuring device (trade name "DynTIM", manufactured by Siemens KK), the thermal resistance of the electromagnetic wave absorbing thermally conductive sheet prepared using three types of spacers was measured when it was compressed by 20% in the thickness direction (i.e., compressed to a thickness of 80% of the original thickness). The thermal conductivity was then calculated from the slope of the extrapolated line of the thermal resistance value obtained for the electromagnetic wave absorbing thermally conductive sheet of each film thickness. Note that if the sheet could not be molded, it was marked "N / A" (measurable).

[0068] (2) Dielectric Loss For the electromagnetic wave absorbing thermally conductive sheet produced using a 1.5 mm spacer, S parameters were measured at a frequency of 28 GHz by the free space method using a microwave network analyzer (product name "N5222B", manufactured by Keysight) and a free space measurement device (product name "FS-330", manufactured by EM Lab Co., Ltd.). The relative permittivity (εr') and dielectric loss tangent (tanδ) were calculated from the obtained S parameters, and the dielectric loss was calculated using these values. Note that if sheet molding was not possible, it was marked as "N / A" (measurable).

[0069]

[0070] As can be seen from Table 1, the electromagnetic wave-absorbing heat-conductive sheets of the Examples had a thermal conductivity of 3 W / mK or more in the thickness direction when compressed by 20%, indicating excellent thermal conductivity, and a dielectric loss of 3000 dB / m or more at a frequency of 28 GHz, indicating excellent electromagnetic wave absorption characteristics in the millimeter wave band. On the other hand, the electromagnetic wave-absorbing heat-conductive sheet of Comparative Example 1 had a dielectric loss of less than 3000 dB / m at a frequency of 28 GHz, indicating poor electromagnetic wave absorption characteristics in the millimeter wave band. Furthermore, it was not possible to mold an electromagnetic wave-absorbing heat-conductive sheet in Comparative Example 2.

[0071] Variations of the present invention are described below. [Appendix 1] An electromagnetic wave-absorbing heat-conductive sheet comprising a binder component and powder, having a thermal conductivity of 3 W / mK or more in the thickness direction when compressed to 80% of its original thickness, and a dielectric loss of 3000 dB / m or more at a frequency of 28 GHz. [Appendix 2] The electromagnetic wave-absorbing heat-conductive sheet according to Appendices 1, wherein the powder comprises silicon carbide and / or zinc oxide. [Appendix 3] The electromagnetic wave-absorbing heat-conductive sheet according to Appendices 1 or 2, wherein the binder component content is 2 to 40 mass % and the powder content is 60 to 98 mass %. [Appendix 4] The electromagnetic wave-absorbing heat-conductive sheet according to any one of Appendices 1 to 3, wherein the powder comprises powder (A) having a median diameter of more than 20 μm and not more than 130 μm, and powder (B) having a median diameter of 1 to 20 μm. [Appendix 5] The electromagnetic wave-absorbing heat-conductive sheet according to any one of Appendices 1 to 4, wherein the powder comprises powder (C) having a median diameter of less than 1 μm. [Appendix 6] The electromagnetic wave-absorbing heat-conductive sheet according to any one of Appendices 1 to 4, wherein the powder may comprise powder (C) having a median diameter of less than 1 μm, and the content of powder (A) is 30 to 90 mass%, the content of powder (B) is 10 to 60 mass%, and the content of powder (C) is 30 mass% or less, relative to 100 mass% of the total amount of the powder in the electromagnetic wave-absorbing heat-conductive sheet. [Appendix 7] The electromagnetic wave-absorbing heat-conductive sheet according to any one of Appendices 1 to 6, wherein the binder component is a silicone-based resin.

[0072] REFERENCE SIGNS LIST 1 Electromagnetic wave absorbing heat conductive sheet 2, 3 Release sheet 11 Binder component 12 Powder 12a Powder (A) 12b Powder (B) 12c Powder (C)

Claims

1. An electromagnetic wave absorbing, thermally conductive sheet containing a binder component and powder, which has a thermal conductivity of 3 W / mK or more in the thickness direction when compressed to 80% of its original thickness, and a dielectric loss of 3000 dB / m or more at a frequency of 28 GHz.

2. The electromagnetic wave absorbing, heat conductive sheet according to claim 1, wherein the powder contains silicon carbide and / or zinc oxide.

3. An electromagnetic wave absorbing, heat conductive sheet according to claim 1 or 2, wherein the binder component content is 2 to 40 mass % and the powder content is 60 to 98 mass %.

4. An electromagnetic wave absorbing, heat conductive sheet according to claim 1 or 2, wherein the powder comprises powder (A) having a median diameter of more than 20 μm and not more than 130 μm, and powder (B) having a median diameter of 1 to 20 μm.

5. The electromagnetic wave absorbing, heat conductive sheet according to claim 4, wherein the powder comprises powder (C) having a median diameter of less than 1 μm.

6. The electromagnetic wave absorbing heat conductive sheet according to claim 4, wherein the powder may contain powder (C) having a median diameter of less than 1 μm, and the content of powder (A) is 30 to 90 mass%, the content of powder (B) is 10 to 60 mass%, and the content of powder (C) is 30 mass% or less, relative to 100 mass% of the total amount of the powder in the electromagnetic wave absorbing heat conductive sheet.

7. The electromagnetic wave absorbing, heat conductive sheet according to claim 1 or 2, wherein the binder component is a silicone resin.

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